sw64: iommu: fix the mask of physical address when flushing pcache

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6ILC2



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PCACHE_FLUSHPADDR reg specifies addr[47:7] of the physical address
of the pte to be flushed, and other bits reserved, so we can write
the physical address directly into the reg.

Signed-off-by: Zheng Chongzhen <zhengchongzhen@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>